Exp#5 Qualitative Analysis

Exp#5 Qualitative Analysis - EXPERIMENT 5 Semimicro...

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Experiment 5- Page 1 EXPERIMENT 5 Semimicro Qualitative Analysis INTRODUCTION A complete chemical analysis of a sample focuses first on what is in the sample (a systematic study called qualitative analysis). Once the chemist knows which substances are present, then a quantitative analysis is performed to determine how much of each substance is present. Many times the chemist has only a limited amount of sample with which to work and analytical procedures must be done on a semimicro or micro scale. Instrumental techniques can often be used in such cases. Techniques based on wet chemistry, however, are often simpler and can be used to quickly analyze a sample (at least for semiquantitative analyses). In this experiment, you will investigate a mixture of ten common metal ions. This is best accomplished by studying them first individually to determine typical reactions for each ion. In the second part of the experiment, you will be given an unknown sample that may contain from one to ten of these metal ions. The goal will be to follow a procedure to separate them first into several groups, each of which contains ions exhibiting a common chemical property that is the basis of the separation based on solubility. Specific tests will then be run to determine individual components of the mixture. For comparison purposes, you will run all tests in Part II of this experiment on both your unknown sample and a "control" sample (sometimes colloquially called a ' known '). This "control" sample will contain all of the ions in question. By comparing the results from you unknown sample to the definitive results from your "control" (or ' known ') sample, you will be able to determine whether a particular ion is present in your unknown (i.e., if your unknown behaves exactly the same way as your "control", then the ion in question is present in your unknown . If, on the other hand, you obtain a positive result from your "control" but nothing happens with your unknown , then that ion is not present in your unknown ). For the best comparison, it is strongly advisable that you run all tests on both your "control"/ known and unknown samples simultaneously. The theory behind the separation and identification of ions in the qualitative analysis scheme presented in this experiment follows a series of important concepts that you learned in lecture. Ionic equilibria, complex ion formation, solubility products and oxidation reduction reactions will all enter into the scheme of separation. Make certain that you understand the chemistry behind the reactions involved. Remember that you will use the concepts of K sp , ion product ( Q sp ), p H, weak acid-weak base complexation in this experiment. Many separations will involve the formation of insoluble precipitates. Although no species is totally soluble or insoluble, generalized solubility rules can be made for aqueous solutions, which include: WATER-SOLUBLE SALTS 1. All salts containing the chloride ion, Cl , bromide ion, Br
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This note was uploaded on 09/14/2009 for the course CHEM 6B taught by Professor Crowell during the Spring '08 term at UCSD.

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Exp#5 Qualitative Analysis - EXPERIMENT 5 Semimicro...

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